I'm figuring they hide somewhere in here:

I'm beginning to play with this here, by making a box and then getting the positions and then the texcoords
#get vertices colours for later nefarious work
boxy_colour = vrFieldAccess(boxy.fields().getFieldContainer("texCoords7"))
which will then require a list of vertex colours with rgb and gamma as vec4f or something along those lines. I'm just getting started so it's slow going...
check Simon Nagel's 'load point cloud script' (that I'm using for a lunch hour project that is taking more than my lunch hour 🙂 )
https://github.com/simonnagel/VRED-loadPointCloudPTS
He accesses the vertices and maps the rgb from a point cloud, so i guess this might help put you on track.